A portable lighting device is known which may be switched between the continuous lighting mode and the intermittent lighting mode by a switching operation. A portable flashlight is also known which may be lit only while a pushbutton switch is depressed. However, when transmitting with these conventional portable flashlights, Morse signals representing "SOS" (dot, dot, dot, dash, dash, dash, dot, dot, dot), the pushbutton switch must be depressed the number of times and durations necessary for generating these signals. Furthermore, the relative ratio of the dot and dash signals of the Morse signal to the blank periods therebetween is controlled manually, resulting in inaccuracy. In particular, in the case of an emergency such as an accident or distress, it may not be possible to manually transmit signals to somebody else. When signaling an SOS with a portable flashlight by manually switching on and off the flashlight, or by flashing non-periodically with the use of a bimetal or the like, the signaling may simply be regarded as mischivous behavior or a greeting between boats or the like. This makes it impossible to prevent disastrous accidents or to rescue people from such accidents.